Electromagnetic shielded door structure



, April 21, 1970l D. CLARK :TAL 3,507,974

LEOTROMAGNETIC SHIELOEO DOOR STRUCTURE Filed March 6, 1968 3Sheets-Sheet l mvENToRs. .CLARK THEOOORE J. ROSTER BY DON `rsRvuN F;JOHNSTON ATTORNEY.

Y Q f v` j., Plll 21, 1970 o. B. CLARK ETAL- l ELECTROMAGNETICsHIBLDEDpooR STRUCTURE Filed March 6, 1968 3 Sheets-Sheet 2 April 21,1970 D. B. CLARK ET AL ETIc SHIELDED DOOR STRUCTURE ELECTROMAGN FiledMarch 6, 1968 5 Sheets-Sheet 5 om mm N m @N mw Nm oo. No. w.

United States Patent O 3,507,974 ELECTROMAGNETIC SHIELDED DOOR STRUCTUREDon B. Clark, Ventura, and Theodore J. Roster, Oxnard, Calif., assignorsto the United States of America as represented by the Secretary of theNavy Filed Mar. 6, 1968, Ser. No. 710,948 Int. Cl. H05k 9/00; E06b 7/23U.S. Cl. 174-35 7 Claims ABSTRACT OF THE DISCLOSURE The descriptiondiscloses an electromagnetic shielded door structure wherein the doorhas a peripheral groove about its edge and means disposed within thegroove for electromagnetically shielding the door when in a closedposition. Such means may include elongated finger stock which isflexible so as to engage a door frame in a flexed position and todisengage the door frame in a relaxed position; and an elongated bladderwhich is `inflatable to force the finger stock to its flexed position inengagement with the door frame and deflatable to allow the finger stockto relax to its disengaging position.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment 'of any royalties thereon or therefor. l

Electronics equipment which is carrying classified information or whichwill electromagnetically interface with other nearby electronicsequipment is often shielded by an enclosure. In order to gain access tosuch an enclosure an electromagnetic shielded door is employed which hasa metallic strip or finger stock mounted around its edge to makeelectromagnetic sealing contact with a metallic door frame. Previouslyexisting shielded doors have the finger stock mounted exteriorly aboutthe edge of the door which has caused several problems. One maindisadvantage is that the finger stock protrudes from the edge of thedoor when it is open which allows the finger stock to become easilydamaged by nearly foreign objects as well as passing personnel whocannot resist the temptation to give the delicate finger stock a littletwist. This finger stock upon becoming bent will leave an area ofdisengagement between the finger stock and the metallic door frame whichallows stray electromagnetic waves to escape from the shieldedenclosure. Once the finger stock has become bent out of shape it isnormally necessary that.

the entire strip be removed and replaced which is a time consuming andexpensive process. Another disadvantage of exteriorly mounted fingerstock is that the door is very diflicult to push open and closed becauseof the wiping action between the finger stock and the metallic doorframe. This wiping action is necessary to clear the metallic componentsof' oxides and films deposited thereon so that at the place of theirengagement an electromagnetic seal can be effected.

The patent to Dunn entitled Doors for Radio Shielded Enclosures, PatentNo. 2,757,225, discloses an approach where difficult door opening andclosing can be obviated. While Dunn mounts exteriorly his finger stockto the edge of the door, he utilizes an inflatable bladder for flexingthe finger stock into engagement with the metallic door frame after thedoor has been closed. In solving one problem, however, Dunn createsanother problem, name- 3,507,974 Patented Apr. 21, 1970 ily damagedwhile the door is open and will become diflicult to replace once it hasbeen so damaged.

The present invention provides an electromagnetic shielded door whichovercomes the aforementioned problems of prior art shielded doors bymounting an inflatable bladder and the finger stock within a groovewhich extends about the edge of the door. The finger stock is flexibleenough to engage the door frame in a flexed position and to disengagethe door frame in a relaxed position. The inflatable bladder retains thefinger stock within the groove and upon becoming inflated forces thefinger stock to its flexed position in engagement with the door frameand upon deflation allows the finger stock to relax to its disengagingposition. In this manner the door can be easily opened and closed andthe finger stock can be controlled to make the necessary electromagneticseal after the door is in its closed position. When the bladder isdeflated the finger stock can be easily removed and replaced whendesired. By disposing the finger stock entirely Within the groove whenthe bladder is deflated the finger stock will be protected from damageby outside elements. By employing finger stock which is generallyU-shaped in crosssection, a good wiping action can be obtained when oneleg of the finger stock is forced against the metallic door frame by theinflated bladder. This wiping action can be increased by slightlyconvoluting the finger stock. Further, by an unusual configuration ofthe bladder and the finger stock we have been able to obtain an acousticseal around the edge of the door in addition to our electromagneticseal.

An object of the present invention is to overcome the aforementionedproblems of the prior art electromagnetic shielded doors.

A further object is to provide an electromagnetic shielded doorstructure which can be easily opened and closed and which will effectnecessary wiping action between the velectromagnetic sealing components.

Another object is to provide an easily opened and closed electromagneticshielded door which has finger stock which is inaccessible to damage andwhich can be easily replaced.

Still another object is to provide an effective electromagnetic shieldeddoor which is easy to operate.

Yet another object is to provide an effective electromagnetic shieldeddoor which also provides an acoustic seal.

Other objects, advantages andnovel features of the invention will becomeapparent from the 4following detailed description of the invention whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view of the shielded door as seen Ifrom inside theenclosure;

FIG. 2 is a view along plane II-II of FIG. l;

FIG. 3 is a view taken along plane III-III of FIG. l;

FIG. 4 is a view taken along plane IV-IV of FIG. l;

FIG. 5 is a view taken along plane V-V of FIG. 3;

FIG. 6 is a view taken along plane VI-TVI of FIG. l;

FIG. 7 is an enlarged View of the edge of the door and door frame ofFIG. 6;

FIG. 8 is a side view of a nger stock gasket;

FIG. 9 is a top view of the finger stock gasket; and

FIG. l0 is a cross-sectional view of the finger stock gasket.

Referring now to the drawings wherein like reference numerals designatelike or similar parts throughout the ly: providing insufficient wipingaction between the finger stock and the metallic door frame to clearthese metallic comporents of oxides and films. Further, the exteriorlymounted finger stock in the Dunn patent can become easseveral views,there is shown in FIGS. 1 and 2 an electromagnetic shielded doorstructure 10 which includes a door which is hung in a door frame 14 byany suitable means such as a hinge 16. The door 12 provides access to acompartment or enclosure 18 which is adapted to enclose radio frequencyelectronics equipment (not shown). The enclosure 18 as well as the door12 are constructed of a radio frequency shielding material. The materialwhich may be employed for the door 12 will be described in more detailhereinafter. Upon closing the door 12 it is imperative that the edge 20thereof provide an electromagnetic seal with the door frame 14 so thatstray radio frequency waves cannot escape from the enclosure 18.

As shown in FIGS. 6 and 7, our invention obtains an uniqueelectromagnetic seal between the edge of the door 12 and the door frame14. The door frame 14 may 4be constructed of angle irons and connectedto these angle irons by any suitable means, such as bonding or spotwelding, may be brass plates 22 which extend around the entire edge ofthe door 12 adjacent and in close proximity to the door edge 20. Theentire door edge 20 is provided with a groove 24, or as shown in ourexemplary embodiment, a pair of such grooves 24. These grooves may beconstructed in the door edge 20 by any suitable means such as mountingchannel members 26 to the edge of the door by screws 28 which extendthrough the base ofthe channel members into the door body.

1n order to make an electromagnetic seal With the plate 22 elongatedlinger stock gaskets 30, as shown in detail in FIGS. 8 through 10, maybe disposed within each channel member 26. The linger stock 30 isflexible in its transverse plane and may be generally U-shaped in crosssection when in a relaxed position. The linger stock may be constructedof any suitable shielding material such as a beryllium copper alloy. Asshown in the top channel 26 of FIG. 7, the finger stock 30 in itsrelaxed condition may have one leg 32 which engages one leg of thechannel 26 in a generally parallel fashion and another leg 34 which maybe entirely disposed within the channel 26 opposite to and indisengagement with the brass strip 22. As shown in the bottom channel 26of the FIG. 7, the leg 34 of the finger stock has been flexed to anengaging position with the brass plate 22 so as to make anelectromagnetic seal therewith. In the actual operation of the inventionboth linger stocks 30 are either in a relaxed position or a llexedposition and they are shown in FIGS. r6 and 7 in different positionsonly for description purposes.

Also disposed within each channel 26 is an elongated inflatable bladder36 which, in both its dellated and nllated condition, engages the fingerstock leg 32 and forces it into retaining engagement with the leg of thechannel 26. As shown in the bottom channel 26, the bladder 36 isinflatable to force the linger stock to its llexed position so that thelinger stock leg 34 is in engagement with the brass plate 22 and, asshown in the top channel 26, the bladder is dellatable to allow thelinger stock to relax to its disengaging position so that the fingerstock leg 34 is located within the channel and disengaged with respectto the brass plate 22. With this arrangement, upon inflation of thebladder 36, the linger stock leg 34 will wipe across the ybrass plate 22toward the center of the door so as to clean these metallic componentsof any oxides and films and thereby make a tight electromagnetic sealtherebetween. This seal may be enhanced by providing the linger stockleg 34 with a convolution as shown in FIG. 7. The other legs 32 of thelinger stock may also be convoluted so that it may be more easilyretained within the channel 26 by the bladder 36. It is to be understoodthat a seal may be accomplished by means other than linger stock, suchas an elongated gasket which is generally U-shaped in cross section.

As shown in FIG. 7, the bladder 36 may be generally rectangular in aninflated condition and may be provided with an elongated centrallylocated recess 38 in its deflated condition. The recess 38 is oppositelydisposed from the brass plate 22 and the finger stock leg 34 may extendwithin this rcess. The linger stock leg 34 may stop short of fullextension across the bladder 36 or the channel 26 so that when thebladder is inflated, as shown in 4 the bottom channel 26 of FIG. 7, aportion of the Ibladder 36 directly engages the brass strip 22. In thismanner an acoustic seal is effected in addition to the electromagneticseal previously discussed. The means for inllating and deflating thebladders 36 in order to effect these seals will be described in detailhereinafter.

In order to lock the door 12 a latch mechanism may be provided on theinside yof the door. As shown in FIG. 6, this mechanism may include alatch plate 40 which may be connected to the frame angle iron 14 by anysuitable means such as Welding. The latch 40 may be provided with anopening and the angle iron 14 may be provided with a similar alignedopening for receiving a latch pin 42. The pin 42 may be slidablelongitudinally within an elongated housing 44 Which is mounted to theinside surface of the door 12 by any suitable means such as an integralllange which is fixed to the door :by screws 46. A pair of such latchmechanisms 44 may be employed, a shown in FIG. 1. A means for operatingthese latch mechanisms will be explained in detail hereinbelow.

The bladders 36 and the latch mechanisms 44 may be operated by a fluidpressure system which may be either pneumatic or hydraulic. This system,which is best illustrated in FIGS. 1 through 5, may include feeder lines48 and 50 which are connected to respective bladders 36, and feederlines 52 and 54 which are connected to respective latch mechanisms 44.These feeder lines may be lluid connected by T connectors 56 and thelines may be mounted against the inside surface of the door by anarcuate flanged member 58 which is screwed against the door. FIG. 4illustrates the connection of the feeder line 48 to the one bladder 36and FIG. 3 illustrates the connection of the feeder line 50 to the otherbladder 36. Both of these feeder lines extend into the internalstructure of the door 12 and may have a central tube 60 which extendsinto the interior of the respective bladder 36 under forced sealingengagement and may have an exterior rubber-like insulative covering 62which seals against the exterior of the respective bladder.

As shown in FIG. 6, the internal tube of the line 52 may be connected tothe latch housing 44 by a fitting 64. The pressure from this tube mayoperate on a piston (not shown) which is located within the latchhousing 44 and is operatively connected to the latch pin 42. This pistonmay be biased by a spring (not shown) which withdraws the latch pin 42from the latch 40 when pressure is not applied to the latch housing 44through the line 52. The connection of the line 54 to the other latchmechanism 44 may be the same as described for the line 52.

The feeder lines 48, 50, 52 and 54 may be fluid connected to a pair ofpush button fluid valves 66 and 68, as shown in FIGS. 1 and 3. A lluidline 70 may extend between the bottom T connection 56 and the top pushbutton valve 68, as shown in.FIGS. 1 and 3. The push button valves 66and 68 may be interconnected by a fluid cross-over line 72 which extendsthrough the door 12. Connected to the push button valve 68 is a pressuresource fluid line 74 which will be described in more detail hereinafter.Each of the valves 66 and 68 have a push button 76 which operatesagainst a spring biased hollow cylinder (not shown) within each of thevalves. When the push button-76 of either of the valves 66 and 68 ispushed pressure from the line 72 is bled through openings (not shown) ofthe valves to relieve the pressure Within the bladders 36 and the latchfixtures 44. This will cause the bladders 36 to dellate and the latchpins 42 to withdraw to their unlocked positions.

When the push buttons 76 of the valves 66 and 68 are in their normalpositions the pressure source line 74 applies pressure through thevalves 66 and 68 and the line 70 to the bladders 36 and the latchfixtures 44. As shown in FIG. 1, the pressure source line -74 isconnected to a push button fluid valve 78 which may be employed foractuating pressure to the bladders 36 and the latch fixtures 44. Asshown in FIG. 6, the push button valve 78 may be mounted to the innersurface of the door 12 by a bracket and screw 80 and may be located inthe proximity of the frame angle iron 14 so that its push button will bedepressed for actuation purposes by a set screw 82 which is threadedthrough the angle iron 14. As shown in FIGS. 2 and 6, a pressure line 84may be connected to the push button 78 and may extend through the wallof the enclosure 18 to a Huid pressure source (not shown). Accordingly,when the door 12 is closed the push button fluid valve 78, which issimilar to the valves 66 and 68, is actuated to connect the lines 84 and74 so as to apply pressure to the bladders 36 and the latch fixtures 44as described hereinabove. It is desirable that the latch mechanisms 44be actuated before the bladders 36 are infiated and for this purpose aflow control valve or fiuid restrictor 86 may be interposed in a line 88which connects the feeder lines 48 and 50 to the feeder lines 52 and 54.Accordingly, when the fluid valve 78 is actuated pressure will beforcibly applied to the latch fixtures 44 with a slower buildup ofpressure being applied to the bladders 36.

As shown in FIG. 6 the door 12 may be constructed of a series oflaminations which provide both an acoustic and electromagnetic seal. Thedoor 12 may comprise an interior perforated metallic layer 90, anexterior metallic layer 92, and therebetween there may be a spongerubber layer 94, and an aluminum foil corrugated layer 96 which isfilled with fiberglass 98, a chopped glass fiber and asphalt emulsionlayer 100 and various wooden layers 102. It is to be understood thatmany possible designs may be employed for constructing the door 12.

It is to be understood that the finger stock 30, as illustrated in FIGS.8 through 10, may take various forms with the exception of the generallyU shape, as exemplified in FIG. 10. If desired, the finger stock may besimply a generally U-shaped strip without the various fingers asillustrated in FIGS. 8 and 9.

In the operation of the invention the user simply closes the door andthe push button valve 78 is automatically actuated to apply pressure tothe bladders 36 and the latch fixtures 44. At this time the latch pins42 are quickly actuated to lock the door and the bladders are slower intheir response to inflation due to the control valve 86. Both bladders36 will be inflated and both finger stock gaskets 30 will be forcedagainst the brass plate 22 and in doing so they will wipe toward thecenter of the door to clear both the finger stock gaskets and the brassplate 22 from any oxides and film deposits thereon. This then ensures agood electromagnetic seal between these components. It should be notedthat the door can be easily closed since the finger stock does not comeinto contact with the brass strip 22 until after the door is in a fullyclosed position. When it is desired to open the door the user pushes thebutton of either of the valves 66 and 68 whereupon pressure is bled fromthe latch fixtures 44 and the bladders 36 causing the door to unlock andthe finger stock 30 to disengage the -brass strip 22. It should be notedthat the finger stock legs 34 are withdrawn from a protruding positionwith respect to the edge of the door so as to be substantiallyinaccessible to any damage by foreign objects or users of the door.Further, the manner of retaining the finger stock 30 within the channels26 enables them to be easily replaced if they vshould become damaged.

We claim:

1. An electromagnetic shielded door structure for use with a door frameof a type having an electrically-conductive surface formed peripherallyof the frame adjacent the peripheral edge of a door hung therein, saiddoor structure comprising:

a door provided with an electromagnetic shield, the door having itsperipheral edges formed with a groove having an electrically-conductivefacing disposed in electrical contact with said shield;

an elongate iniiatable and defiatable bladder disposed Vwholly withinsaid groove when deflated;

an elongate electromagnetic gasket having a leg disposed between and incontact with said bladder and said groove facing, said bladder beingformed and disposed in constant engagement with said leg for retainingthe gasket in the groove;

said gasket further having a resiliently-fiexible second leg overlyingsaid bladder and normally disp )sed wholly within said groove in aspaced disengaged relationship with said door frame surface;

said bladder and gasket being so arranged that, when the door is in itshung position, inflation of the bladder presses said second leg intotight engagement with said door frame surface for electrically couplingsaid surface with said door shield; deation of said gasket permittingsaid flexibility-resilient second leg to return to its disengagedposition.

2. The door structure of claim 1 lwherein said gasket is generallyU-shaped in cross-section with its first leg fixedly retained by saidbladder and its second leg disposed for flexing movement about the firstleg whereby inflation of said bladder causes said second leg to move ina swingable manner for producing a wiping and cleaning action on saiddoor frame surface as said inflation progresses.

3. The electromagnetic door structure of claim 2 wherein said second legis convoluted for facilitating said cleanmg'.

4. The electromagnetic shielded door structure of claim 2 wherein:

said bladder has an elongated recess when deflated;

said second leg of the gasket normally being disposed within the bladderrecess.

5. The electromagnetic shielded door structure of claim 2 wherein:

said bladder has a portion which seals directly against said door framesurface when the bladder is iniiated.

6. The electromagnetic shielded door structure of claim 2 wherein eachleg of said gasket is convoluted.

7. The electromagnetic shielded door structure of claim 2 whereinretention of said first leg in the groove is achieved solely byfrictional engagement.

References Cited UNITED STATES PATENTS 2,757,225 7/1956 Dunn 174-35.4

DARRELL L. CLAY, Primary Examiner U.s. C1. X.R. 49-477

